Stacked semiconductor device

ABSTRACT

In a stack type semiconductor device 1, front ends of leads 11 provided at two sides of a first semiconductor device 10 are bent inward to hold a second semiconductor device 20 stacked at the rear surface of the first semiconductor device 10. Since the second semiconductor device 20 is held toward the inside relative to the leads 11 of the first semiconductor device 10, the distance between the outer surfaces of the leads 11 does not increase. Thus, the mounting area does not increase compared to the mounting area required when mounting a single first semiconductor device 10, and furthermore, high density mounting becomes possible by stacking the second semiconductor device 20.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device that is suitablefor high density mounting, and to methods for manufacturing and mountingthis semiconductor device.

In recent years, the rapid technological growth in the field of IC cardsand memory cards has resulted in the need for thinner and more compactresin-sealed semiconductor devices to be mounted in the cards. Inaddition, stack type semiconductor devices achieved by stackingsemiconductor devices over two stages or three or more stages have beenproposed for memory modules and the like.

For instance, DIP (Dual Inline Package) semiconductor devices 100, oneof which is illustrated in FIG. 15, may be employed to achieve a stacktype semiconductor device 103 by stacking the semiconductor devices 100one on top of the other and electrically connecting leads 101 providedat the side surfaces of the semiconductor devices 100 with solder 102 orthe like, as illustrated in FIG. 16. In addition, a stack typesemiconductor device 108 which is achieved by employing an SOJ (SmallOutline J-bend Package) semiconductor device 106 having leads 105 bentin a "J" shape, as illustrated in FIG. 17, stacking a DIP typesemiconductor device 100 on top of it and electrically connecting theirleads 105 and 101 with solder 107 or the like, as illustrated in FIG.18, has also been proposed. These semiconductor devices 106 and 100 areformed thin enough that the semiconductor device 108 has a height thatis equivalent to that of one regular SOJ type semiconductor device. Thestack type semiconductor devices 103 and 108, are each constituted bystacking semiconductor devices over two stages to achieve high densitymounting and can store twice as much information.

However, since the leads 101 must be inserted at through holes to mountthe stack type semiconductor device 103 illustrated in FIG. 16 at asubstrate, double mounting cannot be achieved. Because of this, eventhough the semiconductor device 103 in FIG. 16 is constituted bymultistage stacking, it is difficult to achieve high density mountingsince double mounting is not possible.

In addition, in the stack type semiconductor device 108 illustrated inFIG. 18, the outer surfaces of the solder 107 connecting the leads 105and 101 project out at the two sides to the left and the right. Becauseof this, the distance L107 between the outer surfaces of the solder 107is greater than the distance L105 between the outer surfaces of the SOJleads 105. Consequently, due to the projecting solder 107, the stacktype semiconductor device 108 illustrated in FIG. 18 requires a greatermounting area compared to the mounting area required for mounting thesemiconductor device 106 by itself, which represents an obstacle toachieving high density mounting. In particular, such an increase in themounting area cannot be allowed when ultra high density mounting, inwhich the element footprint is under rigorous restriction, is to beimplemented.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a new andimproved stack type semiconductor device which achieves high densitymounting without increasing the mounting area compared to the mountingarea required when mounting a single semiconductor device, and methodsfor manufacturing and mounting such a stack type semiconductor device.

Another object of the present invention is to provide a new and improvedsemiconductor device that may be employed in an ideal manner in such astack type semiconductor device.

In order to achieve the objects described above, in a first aspect ofthe present invention, a stack type semiconductor device constituted bystacking a plurality of semiconductor devices, which is characterized inthat the front ends of leads provided at the two sides of a firstsemiconductor device located at the outermost position when mounted arebent inward to hold a second semiconductor device that is stacked at therear surface of the first semiconductor device, is provided.

In this stack type semiconductor device, since the second semiconductordevice is held further inward relative to the leads of the firstsemiconductor device, the distance between the outer surfaces of theleads does not increase. Thus, compared to the mounting area requiredwhen mounting the first semiconductor device by itself, no increase inthe mounting area is required, and by stacking the second semiconductordevice, high density mounting becomes possible. Furthermore, a pluralityof second semiconductor devices may be provided, instead of a singlesecond semiconductor device. In other words, there is a possibility withthe stack type semiconductor device disclosed in claim 1 that aplurality of second semiconductor devices may be stacked at the rearsurface of the first semiconductor device.

In such a stack type semiconductor device, it is desirable that theleads of the first semiconductor device be formed in a "J" shape. Byforming the leads in a "J" shape in this manner, a high density typesemiconductor device having several times the capacity of an SOJ typesemiconductor device in the prior art, which has been in wide use, canbe achieved while requiring the same mounting area. Another advantage isthat sockets identical to those for SOJ type semiconductor devices usedin the prior art can be employed for testing. Furthermore, it becomespossible to prevent the leads from becoming deformed. Alternatively,solder balls maybe provided between the leads of the first semiconductordevice and the leads of the second semiconductor device. By melting thesolder balls through heating, the leads of the first semiconductordevice and the leads of the second semiconductor device can beelectrically connected with ease. In this case, if the leads of thesecond semiconductor device are positioned further inward relative tothe leads of the first semiconductor device, the leads can beelectrically connected toward the inside relative to the leads of thefirst semiconductor device to ensure that the solder will not projectout at the two sides to the left and the right of the leads of the firstsemiconductor device and, consequently, that the mounting area will notincrease.

In addition, in order to achieve the objects described above, in asecond aspect of the present invention, a method for manufacturing astack type semiconductor device, which is characterized in that a secondsemiconductor device that is stacked at the rear surface of a firstsemiconductor device, having leads at the two sides thereof, is held bythe front ends of the leads of the first semiconductor device that arebent inward, is provided. By adopting this method, it becomes possibleto manufacture a stack type semiconductor device that achieves highdensity mounting without an increase in the mounting area. It is to benoted that it is desirable to provide solder balls between the leads ofthe first semiconductor device and the leads of the second semiconductordevice.

Furthermore, in order to achieve the objects described above, in a thirdaspect of the present invention, a semiconductor device which ischaracterized in that a lead which lies astride the front and rearsurfaces of the semiconductor device is provided at the two sides of thesemiconductor device. Since the leads of such semiconductor devices,which lie astride the front and rear surfaces of the semiconductordevice, can be abutted with each other with ease simply by stacking thesemiconductor devices, such a semiconductor device is ideal formanufacture of a stacked semiconductor device.

Moreover, it is desirable to provide solder balls at the front surfacesand/or the rear surfaces of the leads in such a semiconductor device.This will make it possible to electrically connect the leads with easesimply by applying heat when manufacturing a stack type semiconductordevice and will also facilitate mounting thereof at a substrate.

Also, in a fourth aspect of the present invention, a stack typesemiconductor device constituted by stacking a plurality ofsemiconductor devices, which is characterized in that a secondsemiconductor device stacked at the rear surface of a firstsemiconductor device located at the outermost position when mounted isheld further toward the inside relative to gull-wing shaped leads at thetwo sides of the first semiconductor device, is provided.

In this stack type semiconductor device in which the secondsemiconductor device is held further toward the inside of the leads ofthe first semiconductor device, the distance between the outer surfacesof the leads does not increase. Thus, the mounting area does notincrease compared to the mounting area required when mounting the firstsemiconductor device by itself. Furthermore, by stacking the secondsemiconductor device, high density mounting becomes possible. It is tobe noted that a plurality of second semiconductor devices may beprovided instead of a signal second semiconductor device. In otherwords, there is a possibility with this stack type semiconductor device,too, that a plurality of second semiconductor devices are stacked at therear surface of the first semiconductor device.

In addition, it is desirable to provide solder balls at the leadspositioned at the rear surface of the second semiconductor device in thestack type semiconductor device described above, since, by melting thesolder balls through heat application, the leads of the firstsemiconductor device and the leads of the second semiconductor devicecan be electrically connected with ease.

Furthermore, in order to achieve the objects described above, in a fifthaspect of the present invention, a method for mounting a semiconductordevice which is characterized in that by positioning a firstsemiconductor device provided with leads at the two sides thereof towardthe outside and positioning a second semiconductor device having solderballs at their leads provided at the rear surface thereof, the secondsemiconductor device is provided toward the inside relative to the leadsof the first semiconductor device at a substrate surface to mount thefirst semiconductor device and the second semiconductor device at thesubstrate surface. By adopting this method, high density mounting isachieved without an increase in the mounting area at the substratesurface. It is to be noted that it is desirable to mount the firstsemiconductor device and the second semiconductor device at thesubstrate surface at the same time.

Moreover, in order to achieve the objects described above, in a sixthaspect of the present invention, a stack type semiconductor deviceconstituted by stacking a plurality of semiconductor devices, which ischaracterized in that leads positioned at the rear surface of a firstsemiconductor device located at the outermost position when mounted andleads positioned at the two sides of a second semiconductor devicestacked at the rear surface of the first semiconductor device areelectrically connected via solder, is provided. It is to be noted that aplurality of first semiconductor devices instead of a single firstsemiconductor device may be provided in such a stack type semiconductordevice. In addition, the leads of the second semiconductor device may beformed in a "J" shape, for instance, so that the same sockets as thoseused with an SOJ type semiconductor device in the prior art can beemployed for testing and that the leads are prevented from becomingdeformed.

Moreover, in order to achieve the objects described above, in a seventhaspect of the present invention, a method for manufacturing a stack typesemiconductor device which is characterized in that a firstsemiconductor having solder balls provided at leads at the rear surfacethereof and a second semiconductor device having leads at the two sidesthereof are stacked with a first semiconductor device positioned on theoutside and the second semiconductor device positioned on the inside andin that the leads of the first semiconductor device and the leads of thesecond semiconductor device are electrically connected by solder, isprovided. By adopting this method, too, it becomes possible tomanufacture a stack type semiconductor device that achieves high densitymounting without an increase in the mounting area.

Furthermore, in order to achieve the objects described above, in aneighth aspect of the present invention, a method for mounting asemiconductor device, which is characterized in that a firstsemiconductor device having solder balls at leads at the rear surfacethereof and a second semiconductor device having leads at the two sidesthereof are stacked at the surface of a substrate, with the firstsemiconductor device positioned on the outside and the secondsemiconductor device positioned on the inside, to mount the firstsemiconductor device and the second semiconductor device at the sametime at the substrate surface, is provided. By adopting this method,too, it becomes possible to achieve high density mounting without anincrease in the mounting area at the substrate surface.

Moreover, in order to achieve the objects described above, in a ninthaspect of the present invention, a stack type semiconductor devicehaving a first semiconductor device provided with a plurality of leadsextending from the two sides thereof and a second semiconductor deviceprovided toward the inside relative to the first semiconductor deviceand having ball electrodes at the rear surface thereof, is provided. Inthe stack type semiconductor device, the ball electrodes may assume astructure in which solder balls are provided at leads positioned at therear surface of the second semiconductor device, for instance. Inaddition, a structure in which the leads of the first semiconductorelement and the ball electrodes of the second semiconductor devicecorresponding to the leads are commonly connected to a conductivepattern formed at the surface of the substrate may be adopted.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the invention and the concomitantadvantages will be better understood and appreciated by persons skilledin the field to which the invention pertains in view of the followingdescription given in conjunction with the accompanying drawings whichillustrate preferred embodiments.

FIG. 1 is a front view of a first semiconductor device which is idealfor application in manufacturing the stack type semiconductor device ina first embodiment of the present invention;

FIG. 2 is a front view of a second semiconductor device which is idealfor application in manufacturing the stack type semiconductor device inthe first embodiment of the present invention;

FIG. 3 is a perspective of the rear surface of the second semiconductordevice;

FIG. 4 is an enlarged cross section along line A--A in FIG. 3;

FIG. 5 illustrates a manufacturing step for manufacturing the stack typesemiconductor device in the first embodiment of the present invention;

FIG. 6 is a front view of the stack type semiconductor device in thefirst embodiment of the present invention;

FIG. 7 is a front view of the semiconductor device in a secondembodiment of the present invention;

FIG. 8 is a front view of the stack type semiconductor deviceconstituted by stacking a second semiconductor device at the frontsurface of the semiconductor device in the second embodiment of thepresent invention;

FIG. 9 is a front view of a semiconductor device in a third embodimentof the present invention;

FIG. 10 is a front view of the stack type semiconductor deviceconstituted by stacking a second semiconductor device at a front surfaceof the semiconductor device in the third embodiment of the presentinvention;

FIG. 11 is a front view of the stack type semiconductor device in afourth embodiment of the present invention;

FIG. 12 is an exploded view illustrating the method for mounting thestack type semiconductor device in the fourth embodiment of the presentinvention at the surface of a substrate;

FIG. 13 is a front view of the stack type semiconductor device in thefifth embodiment of the present invention;

FIG. 14 is an exploded view illustrating the method for manufacturingthe stack type semiconductor device in the fifth embodiment of thepresent invention, while concurrently mounting it at a substratesurface;

FIG. 15 is a front view of a DIP type semiconductor device;

FIG. 16 is a front view of semiconductor devices in a stack typesemiconductor device achieved by stacking DIP type semiconductor devicesvertically;

FIG. 17 is a front view of an SOJ type semiconductor device; and

FIG. 18 is a front view of the stack type semiconductor deviceconstituted by stacking a DIP type semiconductor device at the frontsurface of an SOJ type semiconductor device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is an explanation of the preferred embodiments of thepresent invention in reference to the drawings. It is to be noted thatthe same reference numbers are assigned to components having almostidentical functions and structural features in the following explanationand the attached drawings to preclude the necessity for repeatedexplanation thereof.

FIG. 1 is a front view of a first semiconductor device 10 and FIG. 2 isa front view of a second semiconductor device 20, which are ideal forapplication in manufacturing a stack type semiconductor device 1 in thefirst embodiment of the present invention.

As illustrated in FIG. 1, leads 11 for implementing input/output of anelectrical signal for a semiconductor element (not shown) which isinternally provided in the first semiconductor device 10 are provided atthe two sides to the left and the right of the first semiconductordevice 10. It is to be noted that a plurality of leads 11 are providedat each of the two sides to the left and the right of the firstsemiconductor device 10. In addition, while the leads 11 are each formedin a shape spreading either to the left or the right side of the firstsemiconductor device 10 in the example presented in the figure, theleads 11 may be instead formed to bend downward at a right angle, asillustrated by the broken lines 11' in FIG. 1, for instance.

As illustrated in FIG. 2, the second semiconductor device 20 isconstituted of a semiconductor device which is commonly referred to as aSmall Outline Ball (SOB) semiconductor device. Namely, leads 21 areprovided at the two sides to the left and right at the rear surface (thebottom surface in the example presented in the figure) of the secondsemiconductor device 20. These leads 21 have a length at which the leads21 do not project out to the two sides to the left and right of thesecond semiconductor device 20. In addition, a solder ball 22 which willfunction as an electrical connector when mounting the secondsemiconductor device 20 at a substrate or the like is mounted at each ofthe leads 21.

FIG. 3 is a perspective of the rear surface of the second semiconductordevice 20, and FIG. 4 is an enlarged cross section along line A--A inFIG. 3. As illustrated in FIG. 3, a plurality of leads 21 and aplurality of solder balls 22 are provided over specific intervals atboth sides to the left and right of the rear surface of thesemiconductor device 20. As illustrated in FIG. 4, a semiconductorelement 23 is sealed with resin 24 inside the second semiconductordevice 20. The example in the figure assumes a structure in which theleads 21 are mounted at a surface of the semiconductor element 23 via aninsulating tape 25 and the semiconductor element 23 and the leads 21 aresecured as an integrated unit with the resin 24. The leads 21 areelectrically connected with a terminal 26 formed at a surface of thesemiconductor element 23 via a conductor wire 27 such as, for instance,a gold wire so that input/output of an electrical signal is implementedfor the semiconductor element 23 via the leads 21. In addition, a sourceline 28 for supplying a source current to the semiconductor element 23is provided inside the resin 24.

Next, the stack type semiconductor device 1 in the first embodiment ofthe present invention is explained by following the sequence of itsmanufacturing processes. First, as illustrated in FIG. 5, the secondsemiconductor device 20 is stacked from below at the rear surface (thebottom surface in the example presented in the figure) of the firstsemiconductor device 10. The production of the stack type semiconductordevice 1 will be facilitated if the front surface (the upper surface inthe example presented in the figure) of the second semiconductor device20 is temporarily secured to the rear surface of the first semiconductordevice 10 by using an adhesive or the like at this point.

Next, the leads 11 of the first semiconductor device 10 are bentdownward at a right angle and then the front ends of the leads 11 arebent inward to achieve a "J" shape for the leads 11. It is to be notedthat if the leads 11 are already bent downward, it is only necessary tobend inward the front ends of the leads 11. Thus, as illustrated in FIG.6, the solder balls 22 provided at the two sides to the left and rightof the rear surface of the second semiconductor device 20 are enclosedby the leads 11 of the first semiconductor device 10 so that the secondsemiconductor device 20 is held at the rear surface of the firstsemiconductor device 10.

The stack type semiconductor device 1 in the first embodiment ismanufactured through the sequence described above. It is to be notedthat a further step may be implemented after the above process for heatapplication as necessary to electrically connect the leads 11 of thefirst semiconductor device 10 and the leads 21 of the secondsemiconductor device 20 by melting the solder balls 22.

In the stack type semiconductor device 1 in the first embodimentmanufactured as described above, the second semiconductor device 20 isheld toward the inside relative to the leads 11 of the firstsemiconductor device 10, and since the solder used for connecting theleads 11 of the first semiconductor device 10 and the leads 21 of thesecond semiconductor device 20 does not jut out at the sides, thedistance L11 between the outer surfaces of the leads 11 remains equal toand no greater than the distance between the outer surfaces when thefirst semiconductor device 10 is used by itself. Consequently, themounting area does not increase compared to the mounting area requiredwhen mounting the first semiconductor device 10 by itself, andfurthermore, with the second semiconductor device 20 stacked on it, highdensity mounting becomes possible.

It is to be noted that by forming see leads 11 of the firstsemiconductor device 10 in a "J" shape, as explained in reference to thefirst embodiment, a high density type semiconductor device 1 havingtwice the capacity of an SOJ type semiconductor device widely used inthe prior art is achieved while maintaining an identical external shapeor requiring the same mounting area. In addition, a degree ofconvenience is achieved since the same sockets as those used with SOJtype semiconductor devices in the prior art can be employed for testing.Furthermore, by forming the leads 11 in a "J" shape, the leads 11 areprevented from becoming deformed.

Next, FIG. 7 presents a front view of a semiconductor device 2 in thesecond embodiment of the present invention. It is to be noted that inFIG. 7, a second semiconductor device 30 to be stacked at the frontsurface (the upper surface in the example presented in the figure) ofthe semiconductor device 2 is also illustrated. Since the structure ofthe second semiconductor device 30 is identical to that of the secondsemiconductor device 20 explained earlier in reference to FIGS. 2-4, thesame reference numbers as those in FIG. 2 are assigned to identicalcomponents to preclude the necessity for a detailed explanation thereof.

As illustrated in FIG. 7, leads 31 lying astride the front surface andthe rear surface (the upper and lower surfaces in the example presentedin the figure) of the semiconductor device 2 are provided at the twosides to the left and right of the semiconductor device 2. Input/outputof an electrical signal is implemented for a semiconductor element (notshown) which is internally provided in the semiconductor device 2 viathe leads 31. In addition, solder balls 32 are mounted at the lowersurfaces of the leads 31. It is to be noted that the semiconductordevice 2 in the second embodiment may be constituted by extending theleads 21 of the second semiconductor device 20 explained earlier inreference to FIGS. 2-4 to the front surface, for instance.

Since the leads 31 of the semiconductor device 2 in the secondembodiment lie astride the front surface and the rear surface of thesemiconductor device 2, the leads 31 can be easily abutted with eachother simply by stacking the semiconductor devices 2 to facilitate theproduction of a stack type semiconductor device.

In addition, as illustrated in FIG. 7, for instance, the leads 21 of thesecond semiconductor device 30 can be abutted to the leads 31 of thesemiconductor device 2 simply by stacking the second semiconductordevice 30 at the front surface (the upper surface) of the semiconductordevice 2. Then, by applying heat in this state in which the secondsemiconductor device 30 is stacked at the front surface (the uppersurface) of the semiconductor device 2 to melt the solder balls 22mounted at the leads 21 of the second semiconductor device 30, the leads31 of the semiconductor device 2 and the leads 21 of the secondsemiconductor device 30 can be electrically connected with ease. Thus, astack type semiconductor device 33 constituted by stacking the secondsemiconductor device 30 at the front surface of the semiconductor device2, as illustrated in FIG. 8, can be manufactured.

Furthermore, with the solder balls 32 mounted at the lower surface ofthe leads 31 of the semiconductor device 2, the stack type semiconductordevice 33 manufactured as described above can be easily mounted at asubstrate simply through heat application. It is to be noted that thetotal thickness of the semiconductor device 2 and the secondsemiconductor device 30 stacked together in this stack typesemiconductor device 33 can be reduced by approximately 0.4 mm comparedto, for instance, the stack type semiconductor device 1 explainedearlier in reference to FIG. 6. The total height of the stack typesemiconductor device 33 is approximately 1.2 mm at most and therefore,it is ideal in application in a thin module such as a memory card.

Next, FIG. 9 is a front view of a semiconductor device 3 in the thirdembodiment of the present invention. It is to be noted that in FIG. 9,too, a second semiconductor device 40 to be stacked at the front surface(the upper surface in the example presented in the figure) of thesemiconductor device 3 is shown together. Since the structure of thesecond semiconductor device 40 is identical to that of the secondsemiconductor device 20 explained earlier in reference to FIGS. 2-4except that it is not provided with the solder balls 22, the samereference numbers as those in FIG. 2 are assigned to identicalcomponents to preclude the necessity for a detailed explanation thereof.

As FIG. 9 illustrates, leads 41 are provided lying astride the frontsurface and the rear surface (the upper and lower surfaces in theexample presented in the figure) of the semiconductor device 3 at thetwo sides to the left and right of the semiconductor device 3, as in thesemiconductor device 2 in the second embodiment explained earlier sothat input/output of an electrical signal is implemented for asemiconductor element (not shown) provided internally in thesemiconductor device 3 via the leads 41. However, in the semiconductordevice 3, solder balls 42 are mounted at the upper surfaces of the leads41.

Since the leads 41 lie astride the front surface and the rear surface ofthe semiconductor device 3 in the semiconductor device 3 in the thirdembodiment, too, the leads 41 can be abutted with each other with easesimply by stacking together the semiconductor devices 3 to facilitatethe production of a stack type semiconductor device.

In addition, as illustrated in FIG. 9, for instance, simply by stackingthe second semiconductor device 40 at the front surface (the uppersurface) of the semiconductor device 3, the leads 21 of the secondsemiconductor device 40 can be abutted with the leads 41 of thesemiconductor device 3. Then, by applying heat in this state, in whichthe second semiconductor device 40 is stacked at the front surface (theupper surface) of the semiconductor device 3 to melt the solder balls 42mounted at the leads 41 of the semiconductor device 3, the leads 41 ofthe semiconductor device 3 and the leads 21 of the second semiconductordevice 40 can be electrically connected with ease. Through this process,a stack type semiconductor device 43 constituted by stacking the secondsemiconductor device 40 at the front surface of the semiconductor device3 as illustrated in FIG. 10, is manufactured. Since the thickness of thestack type semiconductor device 43 manufactured in this manner, too, canbe reduced by approximately 0.4 mm compared to that of the stack typesemiconductor device 1 explained earlier in reference to FIG. 6 with itstotal height kept at approximately 1.2 mm at most, the stack typesemiconductor device 43 proves ideal in application in a thin modulesuch as a memory card.

Next, FIG. 11 is a front view of the stack type semiconductor device 4in the fourth embodiment of the present invention and FIG. 12 is anexploded view illustrating the method for mounting the stack typesemiconductor device 4 at the substrate surface. As illustrated in FIG.11, this stack type semiconductor device 4 is constituted by stacking asecond semiconductor device 52 at the rear surface (the lower surface inthe example presented in the figure) of a first semiconductor device 51.The first semiconductor device 51 is constituted of a so-called SmallOutline Package (SOP) semiconductor device. Namely, leads 53 forimplementing input/output of an electrical signal for a semiconductorelement (not shown) that is internally provided in the firstsemiconductor device 51 are provided at the two sides to the left andright of the first semiconductor device 51. A plurality of leads 53,which are formed in a gull-wing shape, are provided at each of the twosides to the left and right of the first semiconductor device 51.

Since the second semiconductor device 52 is structured identically tothe second semiconductor device 20 explained earlier in reference toFIGS. 2-4, the same reference numbers as those in FIG. 2 are assigned toidentical components to preclude the necessity for a detailedexplanation thereof. In the stack type semiconductor device 4, thesecond semiconductor device 52 is held toward the inside relative to theleads 53 of the first semiconductor device 51 by stacking the secondsemiconductor device 52 from below at the rear surface of the firstsemiconductor device 51.

Now, the process for mounting the stack type semiconductor device 4 isexplained in reference to FIG. 12. First, a solder paste 56 is appliedonto footprints 55 (portions where the semiconductor portions areelectrically connected for mounting) formed at the front surface of asubstrate (not shown), and solder balls 22 mounted at the lower surfacesof leads 21 of the second semiconductor device 52 are placed onto thesolder paste 56. Then, by stacking the first semiconductor device 51onto the second semiconductor device 52, the leads 53 of the firstsemiconductor device 51 are placed on the footprints 55 onto which thesolder paste 56 has been applied. By placing the leads 53 of the firstsemiconductor device 51 adjacent to and on the outside of the leads 21of the second semiconductor device 52 in this manner, the secondsemiconductor device 52 is placed toward the inside relative to theleads 53 of the first semiconductor device 51 at the substrate surface.After this, heat is applied to raise the temperature to melt the solderballs 22 mounted at the lower surfaces of the leads 21 of the secondsemiconductor device 52 and the solder 56 applied onto the footprints 55to electrically connect the leads 53 and the leads 21 on the footprints55 and mount the first semiconductor device 51 and the secondsemiconductor device 52 at the substrate surface at the same time.

Since the second semiconductor device 52 is held toward the insiderelative to the leads 53 of the first semiconductor device 51 in thestack type semiconductor device 4 in the fourth embodiment mounted atthe substrate surface in this manner, the distance between the outersurfaces of the leads 53 does not increase. As a result, the externalwidth L of the footprints 55 formed at the substrate surface can remainapproximately equal to the external width L of footprints 58 formounting a semiconductor device (SOP) 57 which is widely employed in theprior art and is also illustrated in FIG. 12 for reference. Thus, themounting area does not increase compared to the mounting area requiredwhen mounting the semiconductor device 57 in the prior art by itself.Moreover, high density mounting becomes possible by stacking the secondsemiconductor device 52. It is to be noted that it is desirable to formthe footprints 55 to extend inward so that the leads 21 of the secondsemiconductor device 52 can be connected to the footprints 55 toward theinside relative to the leads 53 of the first semiconductor device 52.

Next, FIG. 13 is a front view of the stack type semiconductor device 5in the fifth embodiment of the present invention and FIG. 14 is anexploded view illustrating the method for manufacturing the stack typesemiconductor device 5 while concurrently mounting it at a substratesurface. As illustrated in FIG. 13, the stack type semiconductor device5 is constituted by stacking a second semiconductor device 62 at therear surface (the lower surface in the example presented in the figure)of a first semiconductor device 61.

While FIG. 13 illustrates a state in which the solder balls 22 havemelted and become deformed, the structure of the first semiconductordevice 61 is identical to that of the second semiconductor device 20explained earlier in reference to FIGS. 2-4 as clearly illustrated inFIG. 14, and therefore the same reference numbers as those in FIG. 2 areassigned to identical components to preclude the necessity for adetailed explanation thereof. The second semiconductor device 62, on theother hand, is constituted of a so-called SOJ (Small Outline J-bendPackage)semiconductor device. Namely, leads 63 for implementinginput/output of an electrical signal for a semiconductor element (notshown) that is internally provided in the second semiconductor device 62are provided at the two sides to the left and right of the secondsemiconductor device 62.A plurality of leads 63, each bent inward toachieve a "J" shape, are provided at each of the two sides to the leftand right of the second semiconductor device 62. The stack typesemiconductor device 5 is achieved by electrically connecting the leads22 of the first semiconductor device 61 and the leads 63 of the secondsemiconductor device 62 via the melted solder balls 22 in a state inwhich the second semiconductor device 62 is stacked at the rear surfaceof the first semiconductor device 61.

Now, the process through which the stack type semiconductor device 5 ismanufactured while it is concurrently mounted at a substrate surface isexplained in reference to FIG. 14. First, a solder paste 66 is appliedonto footprint 65 formed at the front surface of the substrate (notshown) and the leads 63 of the second semiconductor device 62 are placedin contact on top. Then, as illustrated in FIG. 14, by stacking thefirst semiconductor device 61 onto the second semiconductor device 62after applying a flux 67 on the upper areas where the leads 63 of thesecond semiconductor device 62 are exposed, the solder balls 22 mountedat the lower surfaces of the leads 21 of the first semiconductor device61 are placed on top of the flux 67.After this, heat is applied to raisethe temperature, to cause the solder balls 22 mounted at the lowersurfaces of the leads 21 of the first semiconductor device 61 to melt sothat an electrical connection is achieved between the leads 21 and theleads 63 and also to cause the solder 66 applied on the footprints 65 tomelt to electrically connect the leads 63 with the footprints 65,thereby simultaneously mounting the first semiconductor device 61 andthe second semiconductor device 62 at the substrate surface.

In the stack type semiconductor device 5 in the fifth embodiment, whichis manufactured while it is being mounted at a substrate surface in thismanner, the solder that is used for connecting the leads 21 of the firstsemiconductor device 61 and the leads 63 of the second semiconductordevice 62 almost never jut out onto the sides and thus, the distancebetween the outer surfaces of the leads 63 does not increase. Because ofthis, the external width L of the footprint 65 formed at the substratesurface only needs to be approximately equal to the external width L ofthe footprints 69 used for mounting the semiconductor device (SOP) 68widely used in the prior art which is also shown in FIG. 14 forreference, thereby making it possible to achieve high density mountingwithout having to increase the mounting area. It is to be noted that byforming the leads 63 in the "J" shape, it becomes possible to use thesame sockets as those used with SOJ type semiconductor devices in theprior art for testing and the leads 63 can be prevented from becomingdeformed as well.

According to the present invention, a stack type semiconductor devicewhich achieves high density mounting without having to increase themounting area compared to the mounting area required when mounting asingle semiconductor device is provided. Furthermore, according to thepresent invention, a semiconductor device which is ideal for applicationin such a stack type semiconductor device is provided.

While the invention has been particularly shown and described withrespect to preferred embodiments thereof by referring to the attacheddrawings, the present invention is not limited to these examples and itwill be understood by those skilled in the art that various changes inform and detail may be made therein without departing from the spirit,scope and teaching of the invention.

For instance, the present invention may be adopted in a stack typesemiconductor device constituted by stacking semiconductor devices overthree stages or more instead of two stages. Especially since the leadsof the semiconductor devices 2 and 3 explained in reference to FIGS. 7and 9 are provided lying astride the front and rear surfaces of thesemiconductor devices, the leads can be abutted with each other withease simply by stacking the semiconductor devices and, therefore, proveideal for application in the production of multistage stack typesemiconductor devices.

The entire disclosure of Japanese Patent Application No. 9-215665 filedon Jul. 25, 1997 and Japanese Patent Application No. 9-340660 filed onNov. 25, 1997 including specifications, claims, drawings and summary isincorporated herein by reference in its entirety.

What is claimed is:
 1. A stacked semiconductor device, comprising:afirst semiconductor device; and a second semiconductor device; whereinsaid first semiconductor device includes:a package body having first andsecond main surfaces and a plurality of side surfaces, wherein each ofthe plurality of side surfaces is disposed between the first mainsurface of the package body of said first semiconductor device and thesecond main surface of the package body of said first semiconductordevice; and a plurality of leads, wherein each of the plurality of leadsextends from at least one of the plurality of side surfaces of thepackage body of the first semiconductor device; wherein said secondsemiconductor device includes:a package body having first and secondmain surfaces and a plurality of side surfaces, wherein each of theplurality of side surfaces is disposed between the first main surface ofthe package body of said second semiconductor device and the second mainsurface of the package body of said second semiconductor device; and aplurality of electrodes, wherein each of the plurality of electrodes isdisposed on the first main surface of the package body of said secondsemiconductor device; wherein the first main surface of the package bodyof said first semiconductor device is disposed opposite the second mainsurface of the package body of said second semiconductor device; andwherein each of the plurality of leads has a bend such that each of theplurality of leads is electrically connected to a corresponding one ofthe plurality of electrodes, and said second semiconductor device isdisposed between the leads.
 2. A stacked semiconductor device accordingto claim 1, wherein each of the plurality of leads has an end that isdisposed opposite the corresponding one of the plurality of electrodes.3. A stacked semiconductor device according to claim 1, furthercomprising a plurality of solder balls, wherein each of said pluralityof solder balls is disposed in contact with one of the plurality ofleads and the corresponding one of the plurality of electrodes.
 4. Astacked semiconductor device according to claim 3, wherein each of theplurality of leads has an end that is disposed opposite thecorresponding one of the plurality of electrodes.
 5. A stackedsemiconductor device according to claim 1, further comprising aplurality of footprints formed of a conductive material, wherein each ofthe plurality of leads is disposed in contact with a corresponding oneof the footprints, such that each of the leads is electrically connectedto the corresponding one of the plurality of electrodes through thecorresponding one of said plurality of footprints.
 6. A stackedsemiconductor device according to claim 5, further comprising aplurality of solder balls, wherein each of said plurality of solderballs is disposed in contact with one of the plurality of electrodes andthe corresponding one of said plurality of footprints.
 7. A stackedsemiconductor device, comprising:a first semiconductor device; and asecond semiconductor device; wherein said first semiconductor deviceincludes:a package body having first and second main surfaces andplurality of side surfaces, wherein each of the plurality of sidesurfaces is disposed between the first main surface of the package bodyof said first semiconductor device and the second main surface of thepackage body of said first semiconductor device; and a plurality ofelectrodes, wherein each of the plurality of electrodes extends from thefirst main surface of the package body of said first semiconductordevice to the second main surface of the package body of said firstsemiconductor device, such that one end of each of the plurality ofelectrodes is disposed on the second surface of the package body of saidfirst semiconductor device; wherein said second semiconductor deviceincludes:a package body having first, second, and third main surfacesand a plurality of side surfaces, wherein each of the plurality of sidesurfaces is disposed between the second main surface of the package bodyof said second semiconductor device and the third main surface of thepackage body of said second semiconductor device, and wherein the thirdmain surface of the package body of said second semiconductor device isdisposed between the plurality of side surfaces of the package body ofsaid second semiconductor device and the first main surface of thepackage body of said second semiconductor device; anda plurality ofelectrodes, wherein each of the plurality of electrodes is disposed onthe third main surface of the package body of said second semiconductordevice; and wherein one of the first main surface and the second mainsurface of the package body of said first semiconductor device isdisposed opposite the first and third main surfaces of the package bodyof said second semiconductor device, such that each of the plurality ofelectrodes of said second semiconductor device is electrically connectedto a corresponding one of the electrodes of said first semiconductordevice.
 8. A stacked semiconductor device according to claim 7, whereinsaid first semiconductor device further comprises a plurality of solderballs, wherein each of the solder balls is disposed on a correspondingone of the electrodes of said first semiconductor device.
 9. A stackedsemiconductor device according to claim 8, wherein the first mainsurface of the package body of said first semiconductor device isdisposed opposite the first main surface of the package body of saidsecond semiconductor device.
 10. A stacked semiconductor deviceaccording to claim 8, wherein the second main surface of the packagebody of said first semiconductor device is disposed opposite the firstmain surface of the package body of said second semiconductor device.11. A stacked semiconductor device according to claim 7, wherein thepackage body of said first semiconductor device further includes a thirdmain surface disposed such that the first main surface of the packagebody of said first semiconductor device is disposed between saidplurality of side surfaces of the package body of the firstsemiconductor device and the third main surface of the package body ofthe first semiconductor device.
 12. A stacked semiconductor device,comprising:a first semiconductor device; and a second semiconductordevice; wherein said first semiconductor device includes:a package bodyhaving first and second main surfaces and a plurality of side surfaces,wherein each of the plurality of side surfaces is disposed between thefirst main surface of the package body of said first semiconductordevice and the second main surface of the package body of said firstsemiconductor device; and a plurality of leads, wherein each of theplurality of leads extends from at least one of the side surfaces of thepackage body of said first semiconductor device such that one end ofeach of the plurality of leads is disposed opposite the second mainsurface of the package body of said first semiconductor device; whereinsaid second semiconductor device comprises:a package body having first,second, and third main surfaces and a plurality of side surfaces,wherein each of the plurality of side surfaces is disposed between thesecond main surface of the package body of said second semiconductordevice and the third main surface of the package body of said secondsemiconductor device, and wherein the third main surface of the packagebody of said second semiconductor device is disposed between theplurality of side surfaces of the package body of said secondsemiconductor device and the first main surface of the package body ofsaid second semiconductor device; and a plurality of electrodes, whereineach of the plurality of electrodes is disposed on the third mainsurface of the package body of said second semiconductor device; andwherein the first and third main surfaces of the package body of saidsecond semiconductor device are disposed opposite the first main surfaceof the package body of said first semiconductor device, and each of theplurality of leads is electrically connected with corresponding ones ofthe electrodes by a conductive material.
 13. A stacked semiconductordevice according to claim 12, wherein the conductive material includessolder.